The grant supports a general program of research into the physical properties of nitroxide radical spin-labels used as probes of structure and function of biological systems. Subjects emphasized are: (1) Saturation-Transfer Spectroscopy, (2) the spin-probe--spin-label method, (3) Saturation Recovery, (4) non-equilibrium dynamic processes in model membranes, (5) multi- and differential frequency spectroscopy, and (6) binding tightness of labels to proteins. During the next year special focus will be on pulsed saturation transfer methods and on saturation recovery methods as applied to motion and transport in synthetic and natural membranes.